In the cutting of gears and other toothed articles, such as bevel gears and in particular spiral bevel and hypoid gears, it is common to produce a burr having a sharp, jagged edge at the end of a tooth where the cutting tool exits the tooth slot. Burrs are particularly noted at the end of concave tooth flanks on spiral bevel ring gears and pinions. Regardless of location on a gear, burrs pose an injury risk to a machine operator as well as a performance hazard during subsequent rolling with a mating member. Therefore, it is essential that burrs be removed.
It may also be desirable to provide a chamfer at one or both ends of gear teeth including tip and root ends. After cutting, sharp corners usually exist at the intersection of the tooth sides, tip and/or root with the front and/or back faces and removing the sharp corners makes handling the gear safer and eliminates a potential area of unacceptably high hardness after heat treating.
There are many methods to deburr or to create a chamfer on toothed metal parts. In deburring, a common technique comprises positioning a blade at the edge of the gear while it rotates. The pre-existing burrs are removed by this blade with a scraping action. Processes like these are usually very fast but offer little chance of creating a specific chamfer on the edge of the tooth. The requirements for positioning a deburring blade are lower than in a true cutting process because of the rather simple blade alignment at the outside of the part.
Generally, chamfering methods can be divided into contactless and contacting categories. Contactless processes include thermal energy machining (TEM) and electro chemical machining (ECM). Contacting processes include chamfering with brushes, files, grinders, cutters (including hobbing tools, end mills and disk cutters with cutting inserts), water jet cutters and hydro erosive grinding (HEG). Currently, the most common methods in the gear cutting industry, however, are chamfering with cutters and deburring with deburring blades as discussed further below.
One example of chamfering utilizing a disk cutter is shown in U.S. Pat. No. 7,794,186 wherein the chamfering device is mounted to the column of a gear cutting machine (e.g. machines as shown in U.S. Pat. No. 6,669,415 or 6,712,566) and uses the X and Y motions of the machine for positioning the disk cutter to the tooth flank. Additionally the chamfering device has a pivot axis which offers an angular adjustment. The setup of the chamfering unit is done by the machine operator in a teach mode. That means that the operator aligns the cutter blade manually to the flank of the part in two or three points and the machine calculates a linear path between them. The manual setup is very delicate and the resulting chamfer can be different for each operator depending on his skills. In the actual chamfering cycle the chamfer unit is lowered some distance, e.g. about 6 inches (152 mm), compared to its home position during the primary gear cutting cycle to prevent interferences. Alternatively, a computer-controlled five-axis chamfering unit may be located on the machine column. The setup of such a unit is also done by the machine operator in a teach mode.
Another chamfering arrangement, such as shown in WO 2011/038201, includes a chamfering unit comprising six independent axes all under computer (e.g. CNC) control wherein the unit is positioned adjacent a separate auxiliary spindle and a cut work piece is transferred from the work spindle of the machine to the auxiliary spindle for chamfering. With so many degrees of freedom, a teaching mode for the chamfering may place an undue burden on the operator.
An object of the present invention is to provide a method of chamfering that is essentially automatic and can be performed without a teaching step.